my cultures have never crashed when I started to keep them in containers that weren't letting any light in. Example, I used a butter-spread container which is made up of brown plastic. About once a month, or when I smell it before opening it, I drop in a small handful of oats and yeast, some water, mix it all up and let it sit. I have used tank water, tap water, and distilled water, none seem to matter.
If the smell still persists, I would just take a scoop of it and put it in fresh oats, yeast and clean warm water. As I said, maybe you should try different yeast, as I never had trouble getting microworms to crawl up. My current culture is only a few weeks old(just picked breeding back up) but my last culture was well over 3 years old and I never had to change the medium it was in, I only had to drop in the mix and water every so often and it lived on fine, supported over 3 fry tanks easily.